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Fe-doped ZnO nanoparticles (NPs) with different Fe contents (0.1–5.0 wt%) were prepared using extract of wild olive leaves growing in Saudi Arabia (region of Abha). The biosynthesized NPs were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, Brunauer–Emmett–Teller, scanning electron microscopy, transmission electron microscopy, and photoluminescence (PL). Characterization results showed that undoped ZnO and Fe-doped ZnO powders were crystallized in the wurtzite structure with a small shift for the doped samples. Neither Fe3O4 nor another iron oxide phase was observed in the samples, which proves the incorporation of Fe into the ZnO lattice. Doping has a pronounced effect on the physical and optical properties. Indeed, the size of the crystallites, the energy of the bandgap as well as the intensity of the PL emission decreased with the Fe content. Photocatalytic tests revealed that the doped samples degraded methyl orange (MO) more efficiently than pure ZnO and pure Fe3O4. Moreover, the photocatalytic activity improved with increasing Fe content. The best photocatalyst of the series (Fe–ZnO-5) was found degrading MO by 92.1%, in 90 min in a pseudo-first order reaction.

A series of Keggin heteropolytungstate salts (M1.5PW12O40, M=Cu, Co, Zn and Fe) were prepared and characterized utilizing inductively coupled plasma spectrometry (ICP), Fourier transform infrared (FTIR) spectra, and ultraviolet-visible (UV-Vis) light spectroscopy. The as-prepared catalysts were tested for the oxidation of ethylbenzene by using carbon dioxide/hydrogen peroxide (CO2/H2O2) as the oxidizing agent system under solvent-free conditions. The results indicated that the heteropolytungstates catalyzed the side chain oxidation of ethylbenzene leading to acetophenone as a major product. The effect of various reaction parameters on ethylbenzene oxidation over the best catalyst of the series, namely Co1.5PW12O40 loaded on activated carbon (AC), was investigated. It was found that the selectivity depends strongly on the reaction temperature. Higher reaction temperatures reduce the conversion due to the decomposition of H2O2. Oxidation by a large amount of H2O2 decreases the conversion owing to a decrease of the solubility of ethylbenzene in an aqueous medium, and favors the oxidation of the reaction products, which are more soluble in an aqueous medium. The increase of the CO2 pressure improves both the conversion and the selectivity of acetophenone due to the involvement of the percarbonate species (HCO4−) responsible for oxidation by oxygen transfer.

Gallosilicate zeolite (Ga-Silicate-1) was synthesized and characterized by wet chemical analysis, Fourier transform infrared spectroscopy, X-ray diffraction, BET surface area analysis and 29Si MAS NMR. The prepared Ga-Silicate-1, calcined in the temperature range from 350°C to 550°C, was tested as a catalyst for the synthesis of propylene carbonate (PC) from CO2 and propylene oxide in a solvent-free reaction. The effects of various parameters, such as co-catalyst, reaction temperature, reaction time, and pressure of CO2, on the reaction were investigated. It has been found that increasing the calcination temperature from 500°C to 550°C decreased both the conversion and selectivity to PC from 63.7% to 20.6% and from 77.6% to 58.9%, respectively. Unlike conversion and selectivity, the surface area increased from 96.1 to 103.8 m2/g. This significant increase in surface area due to the degalliation of the zeolite, along with the decrease in conversion, clearly indicates the role of gallium in the production of PC. Under mild reaction conditions (75°C and P(CO2) = 0.55 MPa), a conversion of 70.8% and a selectivity of 81.3% were obtained. Based on the obtained results, a mechanism for the synthesis of PC over the Ga-Silicate-1 catalyst was proposed.